This invention relates to polymers of ethylene. In one of its aspects this invention relates to the formation of water trees in objects formed from compositions of polymers of ethylene used in dielectric applications. In still another aspect of this invention it relates to polymers of ethylene having densities in the medium to high density range, e.g., above about 0.92 g/cc. In still another aspect of this invention it relates to additives for use with polymers of ethylene.
Water treeing can be described as the formation of tree-shaped arrays of microscopic, conductive channels in insulation materials subjected to a combination of high voltage and moisture. The water tree phenomenon is well known and is described in U.S. Pat. No. 4,144,202, incorporated here by reference. Water trees appear to be a serious and growing problem in underground residential distribution electrical cables.
Inhibition of the formation of electrical trees in low density polyethylene (LDPE) has been studied and U.S. Pat. No. 4,206,260 discloses the use of straight and branched chain alcohols having 6 to 24 carbon atoms, most preferably 8 to 12 carbon atoms, as electrical tree inhibitors for low density polyethylene. Low density can be defined as polyethylene having a plurality of branches of various lengths and a density of up to about 0.92 g/cc.
The polymers of ethylene with which this invention is concerned have densities in the medium and high density range--above about 0.92 g/cc, preferably in a range of about 0.935 to about 0.960 g/cc, most preferably in a range of about 0.935 to about 0.950 g/cc. Medium density polyethylene (MDPE) and high density polyethylene (HDPE) are contrasted to LDPE, not only in having a higher density but also in being more linear in nature and exhibiting substantially less structural branching.
It is an object of this invention to provide a method for inhibiting the formation of water trees in objects formed from compositions of polymers of ethylene used in dielectric applications having densities in the medium to high density range. It is still another object of this invention to provide compositions containing polymers of ethylene in the medium to high density range and compounds capable of inhibiting the formation of water trees in objects formed from compositions of polymers of ethylene used in dielectric applications of the compositions.
Other aspects, objects and the various advantages of this invention will become apparent upon reading the specification and the appended claims.